1. Field of the Invention
The present invention relates to a medicinal syringe, comprising                a syringe barrel made of glass or plastic formed with a syringe head, in which either a hollow syringe needle can be integrated or which has a Luer cone, and with a grip plate at its open end;        an elastomeric piston stopper, which is insertable in the syringe barrel, and which has a threaded blind hole for screw connection with a piston rod having a cruciform cross-section; and        a stop for preventing unintended withdrawal of the piston stopper.        
2. Description of the Related Art
It is known to use ampoules and injector bottles for parenteral administration of liquid pharmaceutical products. A medicinal syringe combined with a suitable hollow syringe needle is required for injecting the products contained in these bottles. That means that the liquid pharmaceutical product must be transfer into the medicinal syringe prior to its end use. This process is not only time consuming, but it enables a large number of impurity sources.
In order to guarantee a reliable use of pharmaceutical products, pre-filled one-time-use syringes are available commercially. They permit a rapid injection of the product that they contain after a comparatively simple manipulation or handling. This sort of pre-filled syringe has a syringe barrel made from glass or plastic with a syringe head formed on it, in which either a syringe needle is integrated or which has a Luer connecting cone of a conical connection, if necessary a lockable cone connection (Luer lock). A grip plate is mounted on the other open end of the syringe barrel, either formed in one piece with it or put on it as a separate part. An elastomeric piston stopper is slidable through the open end of the syringe barrel. The piston stopper has a threaded blind hole, in which a piston rod with a threaded front end is screwable in various embodiments. The aforementioned one-time-use syringe, also called a ready-made syringe, with a syringe body made of glass, is described in Norm DIN ISO 11040, in which, for example, the syringe barrel is described in part 4. The elastomeric standard piston stopper and standard piston rod made of plastic with a cruciform cross section are described in part 5.
Pre-filled one-time-use syringes made from plastic are similarly components of standard design and described in numerous references. Especially they have a similar structure, which relates to the piston stopper and the piston rod.
The present invention is based on syringes of the above-described type, which have been put on the market and used to a great extent. The invention is also applicable to syringes, which are not pre-filled, and which, as mentioned above, draw their contents from a bottle in application.
In order to guarantee a problem-free use of the above-describes syringes, other structural features are required because the above-described basic features.
In order to prevent an unintended withdrawal of the piston stopper from the syringe cylinder during the storage, preparation and/or use of the above-described syringe, and/or to guarantee that the uppermost sealing ring of the piston stopper always remains in the syringe barrel, it is necessary to insert a so-called backstop in the syringe body, typically a stop which reduces the diameter of the syringe barrel at its open end. Otherwise the contamination seal of the pre-filled syringe would not be guaranteed.
The state of the art provides different embodiments for this stop.
In the known one-time-use syringe according to DE 100 36 829 A the stop is formed by a ring-shaped constriction of the syringe barrel, which is provided in the filled syringe barrel after insertion of the piston stopper, in order to not prevent insertion of the piston stopper after filling of the syringe.
DE 43 31 137 A provides a stop element mounted on the grip plate end of the syringe on a finger support with enlarged supporting surface in relation to the DIN grip plate. The stop element has at least one projection extending into the syringe barrel, against which the piston stopper impacts or contacts during axial motion toward the open end of the syringe barrel, whereby unintended withdrawal of the piston stopper from the syringe cylinder is prevented. This known stop element formed in the known syringe as a projection, which is in one piece with a finger support, is clamped on the syringe body laterally, so that the projection is inside on the wall of the syringe body in the mounted state. However there is a danger that sufficient fixing of the finger support is not guaranteed based on the clipping of the stop element and the finger support in one piece with it on the syringe body, so that correspondingly the syringe cannot be reliably manipulated by the user, especially during the injection process, and correspondingly can also slip.
U.S. Pat. No. 5,700,247 discloses a syringe, which has a finger support with integrated backstop-function. This finger support is a separate injection molded part, which comprises a base and cover plate, which is pushed on the corresponding DIN grip plate of the syringe body from the outside. The base plate reduced in diameter has a backstop function, which prevents the piston stopper from being erroneously removed from the syringe.
U.S. Pat. No. 4,909,788 and similarly U.S. Pat. No. 5,554,133 disclose a syringe with an elastomeric piston stopper, which has a gripping strip on its open end. An enlarged finger support can be mounted here at this open end, which locks in the said gripping strip, and is subsequently in a press fit, whereby it is can be rotated about the syringe axis.
U.S. Pat. No. 4,072,149 discloses a syringe with a plastic gripping strip, which extends into the syringe body and at the same time forms a stop element for the piston stopper.
Besides this backstop function the piston rod is secured against a rotation in the syringes, so that it cannot be removed in an unintended manner in use. In the process of so-called drawing or aspiration, in which the piston stopper is moved back and forth many times, for example during application of an aqueous solution in a container with a freeze-dried pharmaceutical substance, the piston rod can be lost from the threaded hole in the piston stopper. However this sort of prevention of rotation is not put into action in the above-described state of the art. However U.S. Pat. No. 4,711,637 describes a syringe having a piston rod with a cruciform cross-section, which includes means for prevention of rotation of the piston rod.